The present invention relates to LC filters and, more particularly, to LC filters having a plurality of LC stages and a storage chamber, whereby it is possible to achieve stable and accurate filter characteristics, in a compact package which permits direct observation of the wiring from external to the package, and which is amenable to mass production.
An LC filter of the prior art includes an inductor and a capacitor as discrete components attached to a base. Alternatively, the capacitor is formed on the dielectric base as an electrode which is then coated with an insulating paint. The coil is attached to the capacitor. This procedure is disclosed in Japanese Laid Open Patent Publication No. 58-15223.
It is difficult to control the shape of the coating of insulating paint. When the core of the inductor of the LC filter is formed by painting magnetic and insulating materials on a substrate, the characteristic of the core may be changed by the process of painting and by the solids content of the paint being applied.
The above prior art presents certain problems. Besides the large area on the substrate, the direct attachment of the inductor and capacitor to the substrate complicates making the necessary circuit connections to these elements.
A further problem is that the filter characteristics are sensitive to the positions of the inductors and the directions of their axes. This is due at least partly to electromagnetic coupling between the inductors. Slight angular variation of the axes of the inductors produces substantial variation in the filter characteristics. In the prior art, electromagnetic coupling is reduced by increasing the spacing between inductors. In modern circuits, compact filters are desired. Compact filters require small spacing between inductors. Thus, if the position of an inductor is changed a small amount, either in distance or angle, or both, the filter characteristic may vary too much to be measured.